CI maintenance: clean up cspell.json and Slack notification wiring

[kernelsam]

Summary

Two small CI/config maintenance items for this repo.

1. Remove unused words from .vscode/cspell.json

The words array contains entries that do not appear anywhere in the repository. These are leftover from a shared template or copy-paste from other repos and add noise to the spell-check configuration.

2. Use needs.<job>.result instead of needs.<job>.outputs.status for Slack notifications

Slack notification jobs use needs.<job>.outputs.status to detect failures, which requires the upstream job to explicitly declare an outputs: block with status: ${{ job.status }}. This is unnecessary — GitHub Actions provides needs.<job>.result natively with the same values (success, failure, cancelled, skipped).

Before:

jobs:
  my-job:
    outputs:
      status: ${{ job.status }}
    # ...

  slack-notification:
    needs: [my-job]
    if: ${{ always() && contains(fromJSON('["failure", "cancelled"]'), needs.my-job.outputs.status) }}
    with:
      job-status: ${{ needs.my-job.outputs.status }}

After:

jobs:
  my-job:
    # ...

  slack-notification:
    needs: [my-job]
    if: ${{ always() && contains(fromJSON('["failure", "cancelled"]'), needs.my-job.result) }}
    with:
      job-status: ${{ needs.my-job.result }}